transmission change?

[BillFz1]

Group,
Has anybody here tried to use a late model transmission, like a Tremic or BW. There are many new or high performance models out there. I thought it might be a good idea to kit one up. Since Fiat parts are a bit scarce on the ground. Summit racing has brand new 5speeds for hundreds less that IAP gets for a rebuild! No core charge. The 'Y' for the guibo is the hardest part. Just thinking out loud.
Bill

[So Cal Mark]

the bellhousing might be more difficult than the Y for the driveshaft

[TimpanogosSlim]

the bellhousing might be more difficult than the Y for the driveshaft

Yeah, unless you have access to a CNC and a copy of SolidWorks, bell housing adapting could be spendy.

There are Lada gearboxes that swap in, which is also spendy, and then you have a russian gearbox.

[BillFz1]

Well Slim,
As it happens I'm a mechanical engineer and I work on SolidWorks every day. I can model up things easily. I would need to pay for CNC time but could get a good rate in our shop.
Bill

[aj81spider]

Perhaps I'm incompetent (alright, maybe not perhaps), but when I went to the Summit site the Tremec transmissions were mostly in the $2000-$4000 range. AutoRicambi has a rebuilt Fiat transmission for under $1300 and International Auto Parts has a new Lada transmission for $2000.

While it could be a cool engineering project, unless I'm looking in the wrong place I'm not seeing the cost savings.

[vandor]

Yes, by the time you add up the CAD work and the machining for an adapter, things get expensive. For the output it's likely simpler to just have a custom driveshaft made than to try to adapt the Fiat one to the new transmission.

To me this would be worth while if one could go with a 6-speed trans with OD on both 5th and 6th, hopefully one that is available from salvage yards. Unfortunately Miatas have ratios that are too low.

FWIW we now have new Polish made transmissions for a lot less than our competitors.

[TimpanogosSlim]

Well Slim,
As it happens I'm a mechanical engineer and I work on SolidWorks every day. I can model up things easily. I would need to pay for CNC time but could get a good rate in our shop.
Bill

In that case, go for it. Right now the options are used transmissions, rebuilt transmissions, and lada transmissions. People seem to say that the 124 gearbox is relatively weak and gets chewed up by big power builds, and if the lada gearbox is stronger i haven't heard about it. A few people have swapped in a stronger 131 gearbox which I'm considering for my SC build.

There are probably a dozen or more people on the turbo124 forums who would love to have more options.

[BillFz1]

Slim,
You understand where I was headed with the new transmission idea. There are new 5 speeds designed for V-8s and 3-500 ft/lb of torque that are smaller than the original Fiat tranny. I was thinking of just trying to have a break even on cost with a much tougher late model unit. If the rear end would hold up without the shock absorbing of the guibo, I would love to put in another U joint and toss that sucker.
Csaba,
It is great if you have access to a new fresh-built replacement transmission. I will look on your site. I am still interested in what I would call an upgrade over the original parts. I like the original little Fiat engine, and enjoy the original layout, (unlike my brother who has an RX-7 drive line he is looking at fitting into a spider). My wife is our spiders regular driver, and while we both enjoy it when working well, I just don't want her to be stranded. We installed one of Mark's aluminum radiator kits, which works great BTW. Our focus is toward a more reliable car. We are not focused on originality as much as the original spirit of the car.
Thanks for listening,
Bill

[divace73]

A well maintained Fiat is a very reliable fiat, I often find when 'modifications' are done or lack of maintenance is when issues start to crop up.
I have a 131 box in my car, a bit of fab is needed and tail shaft shortened but is fairly straight forward. However I do track my car every now and then so it does get a bit of abuse.

The fiat box (or any other fiat derived box) if fine for normal day to day driving with a stock engine.

Often the issue is the oil is seldom changed or the wrong oil is put in.

If I was to do a complete gearbox change I'd definitely go for a 6 speed, with the 131 box where I think 5th is 0.8something and a 3.9 ratio diff I still keep going for another gear to drop the revs (only because I use to have a 3.4 diff at once stage and was great for the freeway)

If you go down this path please be sure to update us with your finding and images, I love seeing progress shots, I always got carried away when doing stuff and forget to take photo's.